Thus, today, lighting units with high-performance LED radiation sources are used for example for fluorescence microscopy. It is often necessary to alter the wavelength irradiated into the microscope onto the preparation in order to be able to observe the preparation at different fluorescence wavelengths.
It is known from DE 103 14 125 A1 to arrange LED lighting units that emit light in different colours on a rotatable wheel. The wheel is rotated to change the wavelength. In this solution, electrical contact must be made with the LED radiation sources of the lighting units via sliding contacts in order to be able to supply the corresponding electrical energy for the lighting units.
DE 10 2008 015 720 A1 describes an illuminating device in which the LEDs are fixed and a mirror cascade is rotatable beneath the LEDs. This design is elaborate and requires a large installation space.
US 2008/0310017 A1 describes an illuminating device in which e.g. two LEDs are arranged laterally movable. This, however, requires a large installation space (because of the lateral movement) and the feed lines for the LEDs are moved a relatively long way during the changeover, which results in high wear.